gddo-server: don't tee /_ah/* requests to pkg.go.dev

Currently, requests to App Engine admin paths at godoc.org/_ah/* are not
redirected to pkg.go.dev.

This change stops making a POST request to the teeproxy when a user
visits any of the admin paths.

Change-Id: I77f39b8289eab1086bc987adb218ee55ed48c919
Reviewed-on: https://go-review.googlesource.com/c/gddo/+/235519
Reviewed-by: Julie Qiu <julie@golang.org>
diff --git a/gddo-server/main.go b/gddo-server/main.go
index e25a50f..f02c539 100644
--- a/gddo-server/main.go
+++ b/gddo-server/main.go
@@ -1038,6 +1038,10 @@
 	if f, ok := w.(http.Flusher); ok {
 		f.Flush()
 	}
+	// Don't tee App Engine requests to pkg.go.dev.
+	if strings.HasPrefix(r.URL.Path, "/_ah/") {
+		return
+	}
 	if err := makePkgGoDevRequest(r, latency, s.isRobot(r)); err != nil {
 		log.Printf("makePkgGoDevRequest(%q, %d) error: %v", r.URL, latency, err)
 	}